Process of recovering metals by gaseous reduction



May 12, 1953V w. K. I Ewls 2,633,414

-PROCESS 0F REcovERING METALS BY GAsEoUs REDUCTION Filed July 50, 1948 lOl MELTING,

AIR

.A w/arren Lewis Bnventor B16 QQMMMQEME Patente-d May 12, 195,3

PROCESS F RECOVERING METALSi BY GASEOUS REDUCTION Warren K. LewisyNewton, Mass., assigner to Standard Oil Development Company, a corporation of Delaware Application July 30, 1948, Serial No. 41,604

The present invention is` directed to the production of metals and, particularly, to the recovery of metals from their oxides andk oxidic ores, such as iron from iron ore, nickel from nickel ore, etc.

In the past, efforts have been made to utilize natural gas for the recovery of iron from iron ore. The direct utilization of natural gas, as a reducing agent, is extremely complicated chiefly as a result of the strongly endothermic character ofthe reducing reactions and the diiiiculties encountered in 'supplying the heat required without affecting the eciency of the reducing reaction. The procedure adopted in most cases is, therefore, to convert natural gas by oxidation, reformation or thermal decomposition into more vefiicient reducing gases such as H2 and/or CO and to use these converted gases as the reducing agent.

' For example, it has been suggested to convert natural gas thermally into a gas rich in free hydrogen and thermatomic carbon and suspending powdered iron or in a stream of this gas in such a way that the mixture presents the appearance of a boiling liquidand the powdered iron ore and resulting powdered iron are carried along slowly by the gas stream. Sufficient air is admitted with the hydrogen to produce, by combustion of the latter, sufficient Vheat to maintain the'desired reduction temperature.v The thermatomic carbon may be utilized in melting the `powdered iron produced.' K

Whilethis andfsimilarv fluid solids procedures afford important advantages'with respect to heat economy, ease of materials handling and process control, di'iculties-may be encountered kin controlling vertical back-mixingof fluidized solids and in maintaining the atmosphere within `the entire reduction zone on the reducing side sofas to permit the `recovery of a'fully reduced metallic product in a once-through or single stage process, particularly in continuous operation. Vertical back-mixing resultslin the Withdrawal of a solids mixture. of average rather thanuof highest degree of reduction. A non-reducing or even oxidizingatmosphere-may form'when .the ratio of the partial Apressures,l of hydrogen and Water formed-by the reduction and/or combustion reactionwithin t-he reduction zone drops belowthe minimum atwhich reduction of iron oxides may take place at the temperature involved.

The present invention overcomes the aforementioned difculties and affords various additional advantages. ,These advantages, the nature of the. invention ,and the-manner in which it-y is 13 Claims. (Cl. 75-26) 2 carried out will be fully understood from the following description thereof read with reference to the accompanying drawing. It is, therefore, the principal object of the present invention to provide improved means for recovering metals from their reducible coinpounds.

Another ob-ject of the invention is to provide an improved process for reducing oxidic metal ores with gases rich in free hydrogen.

A more specific object of the invention 4is to provide an improved process for recovering' metals from finely divided oxidic metal oresby reduction with a gas rich in free hydrogen, while maintaining the ore in the form of a dense turbulent mass uidized by an upwardly flowing gas to resemble a boiling liquid forming a well dened upper level. v

Other and more specific objects and advantages will appear hereinafter.

In accordance with the present invention, -a stoichiometrical excess of a gas rich in hydrogen is contacted at a reducing temperature below the sintering point of the metal involved with ra dense turbulent mass of a nely divided reducible solid metal compound iluidized by an upwardly yflow-- ing gas to resemble a boiling liquid having a relatively well defined upper level and the ratio of hydrogen partial pressure to water =partial pressure is maintained at or above the minimum required to establish reducing conditions. This is accomplished by recycling unconverted hydrogen to the reduction zone after the removal of Water from the recycle hydrogen. The heat required to maintain the desired temperature in the reduction zone is supplied as preheat of process solids and' gases and/or by a controlled combustion of hydrogen with air and/or oxygen Within the re-` duction zone. Preferably, the recycle'rate of H2 free of water is so controlled that the partial pressure ratio of H221-I2O leaving the reduction zone proper falls Within the approximate rangeY of from 3 to 2 for reduction temperatures varying.

from about 700 C. to about 900 C. lIn this manner, the invention prevents the buildup of water and thus the formation of a non-reducing or,y oxidizing atmosphere in the iluidized reaction.

The amounts of H2 and oxygen required. to'` establish these conditions depend primarily on fthe type and particle size of the metal compound involved, the heat insulation of the reduction zone and the preheat of the solidsy hydrogen and air. Oxidic iron ores, for example, may be employed in particle sizes Varying from about to 10() microns to be converted by the gases flowing upwardly through the reaction zone at linear velocities Aof 'about 0.3;-5 it. per second into dense, turbulent,"fiu'idized masses having apparent densities of about -150 lbs. per cu. i't. Masses of this type may be successfully reduced in a reduc-V ing zone b-y preheating the ore even up to ternperatures of about 1200o C. and the hydrogen and/or air to about the same temperature and supplying not greatly in excess of the stoichif ometric amounts of hydrogen tothe process. By adequate preheat as described above, together with proper equipment designed to minimize heat losses, the air requirement for the reduction ione may be kept at very low levels or even eliminated entirely.

1.1.1 017431' t9, .eliminate 91' Slbstfimau Edu@ haoisfiiiixios of 'Solids ood 'its idiot-oo ofioots. on the recovery of pure. the'pres vit invention Provides foto. true coautor-Current dow of retiiioiioisi itiotai'ooiiifeoiitio ao iotiiioiiie ,For

this ruinoso, the iiooir oiiidooi iotiii'oiiilio .Solidi in a dense lrluidized state, is passed downwardly through. o vortioitlly oiitoiidios rotiiiotiori Zooo iii ooiiritoioiirront to trio iiofiowitis rotiooiiio soo ooo.

the vertical motion of fluidizedsolids is obstructed.

at. orio or more, iovois oi tiio iooiotoi iiois'iit' loi'ofoi'- ably by taokioss oi 'toetst refractory bodies of iioiiffiiiidiioioio oaitioio sito Wiioii So operating, itf may also. oo desirable toiood at toast o toottaiitiiii Portion of any oii @iid/oi' oxygen, tooo-iro@ vvfoiiioi'it ooooiotioii 'to @intermediate aud/0r upper portion of the re,-l acticn zone. In this manner, a substantial por.- tion or all. oi tito hoot to oo soiooi'ototi Witiiio the reaction chamber may be produced in the l upperrpoi'tioos.. oi the oiioiiiiooi'whiie tito Solid is, Stili, iii the oxide forro Soi that ori @iti-,digits atmosphere iriiioii may iooiiit from o iiisii tio-toi' concentration. may oo iooiiiitoioooi to. oo. disadvantage. The hoot so` goooitoti ttaiisiioifio,il

.assensibl-e heat of the solids to lower Zones v Jhere-` in the roiiuotiiimoy loo oortio-doiit a reoiiioios atmosphere with o i ooit/,- o limito@ otoiiiiotion of;- heat and water by additional controlled cornbostion. However, in. doing this, it is impot-otite to. avoid bringing iiioiooiiosto toiiiooiiii, ooostantial'ly above 900 .after metallic iron has boson to form, Siiioo otiioiwioo; Siiitoiiiis olif-i iiiiiy ization troubles vviii iio oriooiiiitoifodf The site rio-ii tiroirosoo iilSoo ottho too-otitis osent. may. oo orooiioodiirom iiyiiiooorooo gases Such as natural. ses, roditori ses.. methane orv the likeI by s u-ch conventional methods .asy controlled oxidation, thermall or catalytic reforma-f tion with steam and/or C62, or the like. In prac,- tice, it is preferred, however, tosu'bject the hydro-A carbon gas. to. pyrolysisE to convert it into. carbon and hydrogen. ln this case, the. hydrogen pro: ducedis at a temperatureabove. i000? C. whereby the use of: air in the reduction zone` itself-may. be substantially reduced or even completely,A elim,- inated. thermatomic carbon which lends itself readily to introduction into. a flowing stream ot the` powdered product metal for -carbonizati-on yof the..

In addition, the carbon produced is.

of an apparatus suitable for the practice of the present invention.

Referring now in detail to the drawing, the system illustrated therein essentially comprises regenerative hydrogen generation equipment 3, 6, a reduction chamber 30, water separator 54, and metal melting equipment le, and 85, whose functions and cooperation will be explained forthwith using the reduction of an iron ore such as magnetite, hematite or the like with hydrogen produ-ced vfrom natural gas as an example. It should be understood, however, that the apparatus shown may be applied in a substantially analogous manner to the reduction of oxidic ores of other metals.

In operation, hydrogen is produced from natural ygas in the regenerative gas pyrolysis chambers 3` and 6 which are operated alternately in a `Ciiwerltional manner. To start up the procedure, a mixture of natural gas and air in a suitable proportion for high temperature combustion may be vintroduced through lines i and .2 into chamber 3 which is, preferably, packed with a refractory material of high heat capacity such as brick or the like. The combustion mixture is burned within chamber 3 and flue. gases are withdrawn overhead through linge il. When the packing of chamber 3 has reached aI temperature suitable forthe Pyrolysis of methane, say about 1100a tol 13,00o C., line 2 is closed and the con bustion mixture. is passed from line l through line 5 into, chamber 6 from which flue gases are withdrawn through line l8. Simultaneously, sub stantially dry natural gas is fed from manifold l@ through line I I, tochamber 3. wherein pyrolysis methane into H2 and thermatomic carbon takes place. A suspension of carbon in H; andv small amounts of unconverted methane is withdrawn from chamber 3 through line lil and passed sub-` stantially at the temperature of the` pyrolysis to thel ore reduction system. When thetemperature. of. chamber 3. has fallen substantially below 1100"' C., line 5, is closed` and line 2 reopened and the. natural gas feed is divertedvfromline i l and chamber 3 to linefl 2 and. chamber 6. which mean.. whileihas ybeen brought to pyrolysis temperature. Carbon vand H2y from chamber pass thrQueh line |13 andling 1.4. to thel ore reduction` system. inY this manner, a substantially continuous dow o high temperature hydrogen and carbon tothe system may.` be sustained.

The suspension of carbon in hydrogen ilows to a conventional gas-solids separator, such as cyclone. separator L8. Carbon" is withdrawn downwardly from separator [8. through an aerated standpipe 20,I or the like, to` be used-asA will be oXPloinotihoroiiiof-toh Process-hydrogen or our other noiifoxidiziiie eas; may bof supplied through taps 2l for aeration purposes.

Hydrogen is Withdrawn. overhead: from sep-A traitorl i8 andinas'. be. passed without substantial heat loss through lines 22A and 24 to the bottom` S through linev to a preheater |03 which may have the form of a rotary kiln. Excess hydrogen entering line 23 as will appear more clearly hereinafter may be passed through line to a burnerL |01 to which preheated air may be fed through line |09, sufficient 'in amount to burn lthe hydrogen in burner |01. Hot combustion gases from burner |01 may then be passed to kiln |03 and preheat the ore in countercurrent bow. Cold flue gases may be withdrawn through line Preheated ore passesfrom preheater |03 through line 28 to reactor 30. It is noted, however, that this preheating method is suitable only for ores having a high state of oxidation.

When ores of the FeO oxidation stage, such as.

siderite are used undesirable oxidation would take place during the preheating treatment with hot combustion gases. ferred, therefore, to use the sensible heat of spent reducing gas which may be branched off lin'e 48 through line ||3 and supplied as such to preheating kiln |03.

The iron ore entering reduction chamber 30 is converted byv the upwardly flowing hydrogen and gaseous reduction products into a dense, turbulent, iiuidized mass resembling a boiling liquid having an upper level L. For this purpose, the dimensions of reduction chamber 30 are so chosen that substantial reduction of iron ore to metallic iron may take place during the downward passage of the metal through reduction chamber 30 at a temperature of about 100 to 900 C. and at lineary gas velocities within chamber 30 of, preferably, about 0.1 to 1.5 ft. per second to establish apparent phase densities within chamber 30 of about 70 to 125 lbs. per cu. ft. The amount of hydrogen fed to the bottom of chamber' 30 is so controlled Vas to maintain the ratio of Hz to water vapor leaving the nal reduction zone of chamber 30 within -the range specified above.

In accordance with the preferred embodiment of the invention, one or more packings 32 of coarse refractory bodies of non-fluidizable'particle size are arranged at intervals over the.

length of chamber 30. These packings may be composed of Raschig rings, Berl saddles, or the like having diameters of about 1-3 in.A and consisting of clay, chamotte, ceramics, or similar material. These packings vpermit an upward flow` of the gas and downward passage of finely divided ore and simultaneously limit the vertical back-mixing of iiuidized solids across the height of the packings. The overall downward motion of the iiuidized solids is accomplished by the continuous feed of solids to the top through line 28 and continuous withdrawal of solids through line 34 from the bottom of chamber 30, as a result of the pseudo-hydrostatic pressure exerted by the iluidized mass. This arrangement assures true countercurrent iiow of solids and gases and the withdrawal of metal of the highest rather than of average degree of reduction through line 34. Depending on the linear ve` locity of the gases, the unit may be so operated that chamber 30 is lled with a substantially continuous iiuidized mass having a single top level L or so that several fluidized beds are 'formed having individual levels between the packings.

If the preheaty of the hydrogen and iron ore is insuicient to maintain thedesired reduction temperature withinchamber 30, air and/or oxygen may be supplied from manifold 36 through anyone or all of lines 31,-38 and39 andperfo- In this case it is pre-y rated distributing devices 40, 4| and 42, respectively, to generate additional heat within chamber 30 by combustion of excess hydrogen. It is preferred, however, to supply most or all of the air and/ or oxygen to the upper portions of chamber 30 through lines 38 and/or 39. In this manner, most of the heat generated within chamber 30 may be produced in `contact with the fresh ore ina zone in which no or only limited reduction is required and in which even oxidizing conditions may be permitted. The heat so generated is taken up by the ore and transferred to lower sections of chamber 30 wherein reduction may takeplace under the action of substantially pure hydrogen. As a result, less heat needs to be generated in contact with the ore undergoing reduction and the maintenance of a reducing atmosphere in the reduction zone proper is simplified. The amount of air required for this depends on the amount of preheat of the reagents and the heat losses of the system.

The air supplied through manifold 36 is preheated to temperatures preferably up to even l200 C. 'If desired the preliminary stages of this preheat may be secured in heat exchange with the ue gases from pyrolysis units 3 and 6. The total amount of air fed to chamber 30 is so controlled that just enough oxygen is vmade available in chamber 30 to maintain therein a reduction temperature of about 700-900 C.

A mixture of unconverted hydrogen with steam andr traces of CO and CO2 is withdrawn overhead from level L and passed through a conventional gas-solids separator such as cyclone 44 from which separated ore fines are returned through pipe M5k to chamber 30. The gas mixture, now substantially free of ore fines, leaves separator 44 at'a, temperature of about 700-1100 C. depending on the amount and location of the heat generation within chamber 30. The steam content of the gas is determined by the ratio of I-IztHzO employed and by the air consumption, discussed above. y

The hot gases flow through line 48, heat exchanger 50 and condenser 52 to a water separator 54 in' which water is removed by condensation, if desired, in combination with conventional chemical and/or physical drying means. Condensate water maybe withdrawn through line 56 and substantially dry H2 flows through pipe 58 to line 60 from which other impurities maybe purged through vent 02. The purified hydrogen is taken up by blower 64, passed through line 66 and heat exchanger' and returned to hydrogen feed vline 24 or, if desired, to a separate recycle lineleading to the bottom portion of chamber 30. In heat exchanger 50 `the recycle hydrogen is heated up to reduction temperature in heat exchange with the hot off-gas from chamber 30. If desired, additional preheat may be added by'feeding hot combustion gas from burner |01 through line H5 to a preheater H1 through which line 66 passes. Suitable hydrogen recycle ratios may range from about 2 to about 3 volumes of recycled gas per volume of fresh hydrogen supplied. When operating in this manner, the water concentration in the reducing zone of chamber 30 may be readily kept below the limit at which oxidation of metallic iron may take place at the' temperatures involved.

Reduced finely divided metal admixed with gangue is withdrawn under the pseudo-hydrostatic pressure of the dense i'luidized mass of ore inv chamber 30, through bottom vdrawo1fline'34 and passed substantially at reduction-temperature to a melting furnace 1U if desired after the addi tion of thermatomic carbon supplied through standpipe 20 from separator I8. Slag-forming materials may be introduced through line 68, if desired, or if the iron contains ingredients which require their use. The carbon yadded through line 20 serves as the only fuel used in melting furnace TB so that sucient heat may be generated by combustion of the carbon to CO rather than to CO2. In this manner, the maintenance ofv av strongly reducing atmosphere in furnace l is assured and the ofi-gases from furnace lll have a relativelyhigh B. t. u. content which may be utilized to preheat the air required for the heatgenerating combustion in furnace l0.

For the latter purpose, the CO-containing oitgas from furnace lll is passed through lines 1-2 and 'M or '5S alternately to conventional regen,- erative air heaters 89 and 85, respectively, wherein the gas is burned with air supplied through lines 'lll and 79, respectively, to. heat up chambers 8D and 85 to air-preheat temperature. Thereafter, air alone is passed alternatingly through chambersv Si), and 85, Withdrawn there from through lines. Sli and 38, respectively, and passed through line Sil at the desired temperature to furnace lll. Flue gasesk from the burning period may be withdrawn through lines 82 and 34, respectively.

Molten iron and slag may be recovered from the system through lines 92 and 94, respectively. Asthe result of the use of thermatomic carbon in furnace l0, the molten iron may be saturated with carbon, thus substantially reducing its melting point which may be as low as 1100i C. In this manner, the melting furnace may be operated at. low temperature levels of, say, about ll09l3ll0 C. The iron thus produced represents a pig iron suitable for conventional methods of purication.

The-embodiment of the invention described with reference to the drawing permits of Various modiiications. The system may be operated in the pyrolysis and/or reduction stage at atmospheric` or elevated pressures, More than one reduction chamber 3B may be used. Any desired portion or all of the hydrogen withdrawn from I8 may be passed via line 22a and line 23 to join the recycle.

hydrogen in line 6 0; if desirable for` heat-economy or other considerations, A screw conveyor or other conventionall conveying means may take the place of standpipe 2li- Other modicationswilll occur to those skilled in the art without. deviating from thespirit of the invention.

The thermal eiliciencyof the usual processesl ofr reduction oi iron ores to the metal by the use.

of the conventional reducing gases, such asCO containingy gases like water gas, or coal distillation gases, is notoriously low. In. cont-radistinction the energy requrementsfor the production of pig iron when using hydrogen. in accordance with the present invention can be kept down to levels as low as 1A, and in most favorable cased.vr

to as low as 1/3 of the energy requirements for the use of coke inV the conventional blast furnace.

While the foregoing description and exemplary operations. have served to illustrate specific applications and, results of the invention, other modications obvious to those skilled in the art are within the scope of the invention. Only such 'limitations should bev imposed on the invention .as are indicated in they appended claims.

What is claimed is: l. A. method of recovering metal fromy ar solid,

nely dividedcompound thereof which is re-` ducible to metal by hydrogen which comprises maintaining a dense, turbulent mass of said metal compound iluidized by an upwardly flowing gas stream to resemble a boiling liquid having a well defined level Within a reduction zone at a reduction temperature, causing said fluidized mass of metal compound to flow downwardly against the upwardly ilowing stream of gas, limiting the back-mixing of solids in a vertical direction by obstructingr the free, vertical ilow of solids and gases at least at one point along theirvertical path within the reduction zone, contacting said mass with an amount oi hydrogen in excess of that required for reducing said compound to metal, supplying heated nnely divided metal compound particles to said reduction zone, withdrawing a gas mixture containing hydrogen and steam from an upper portion of said reduction zone, removing water from said gas mixture to obtain substantially dry hydrogen, recycling at least a portion of said dry hydrogen to said re duction Zone thereby maintaining the atmosphere in said reduction zone capable of reducing the inely divided metal compound to metal, adding further quantities of hydrogen to said reducing zone and withdrawing reduced metal from a lower portion of said reduction Zone.

2.' The method as dened in claim l wherein said metal compound is an oxidic iron ore.

3. The method as defined in vclaim 1 wherein a limited amount of air or oxygen is supplied to the reduction zone to burn some of the hydrogen therein to generate at least a portion of the necessary heat of reaction.

4. The method as defined in claim l wherein a portion of the hydrogen is burned outside of said reduction zone to generate heat for pre heatmg the inely divided metal compound charge and for preheating the dried hydrogen recycle gas.

5. The method as deiined in claim 1 wherein a limited amount of air or oxygen is supplied to the reduction zone to burn some of the hydrogen therein to generate at least a portion of the necessary heat of reaction and a portion oi the hydrogen-containing gas is burned Outside of said reaction Zone to generate. heat for preheating the finely divided metal compound charge and for preheating the dried hydrogen recycle gas.

6. The process of reducing a nnely divided oxidio metal ore which is reducible to metal by hydrogen which comprises maintaining a dense turbulent mass of said' ore fluidized in a vertical reduction zone by an upwardly flowing stream of gas to resemble a boiling liquid having a well defined level, maintaining said mass at a reduction` temperature, feeding iinely divided ore to an upper portion of said mass, limiting the backmixing of solidsl in a vertical direction by obstructing the free, vertical flow of solids and gases at least at one point along their vertical path, passing upwardly through said mass an amount of hydrogen` in excess of the amount requiredv forl reducing said ore to metal, withdrawing agas mixture containing hydrogenfand. steam from an upper part of said` reduction zone therebyl establishing countercurrent flow of solids and gases within said reduction zone, removing water from said gas mixture to obtain substantially dry hydrogen, recycling said substantially dry hydrogen to the-reaction zone, supplying fresh hydrogen to said reaction Zone in sucient amount to provide said excess` of hydrogen in the reaction zone and correlating the supply of fresh hydrogen and the recycling of dry hydrogen to control the 9 ratio of the partial pressure of hydrogen to the partial pressure of steam in the gas mixture withdrawn from the reduction zone thereby maintaining the atmosphere in said reduction zone capable of reducing the iinely divided metal ore to metal and of preventing reoxidation of reduced metal within the reduction zone and withdrawing reduced metal from the bottom of said reduction zone.

7. Theprocess as dened in claim 6 in which back-mixing of solids in a vertical direction is limited by means of a packing of bodies greater than uidizable particle size whereby the average degree of reduction of the product withdrawn from bottom of the reduction zone is substantially greater than that of the product in the upper portion of the reduction zone.

8. The process as dened in claim 7 in which said ore is an iron ore.

9. The process as defined in claim 6 in which said ore is an iron ore.

10. The process of recovering a metal from a finely divided oxidic metal ore which is reducible to metal by hydrogen which comprises thermally decomposing a hydrocarbon gas at a decomposition temperature to form hydrogen and thermatomic carbon, separating said hydrogen from said carbon, maintaining a dense, turbulent mass of said ore fluidized in a vertical reduction zone by an upwardly flowing stream of hydrogencontaining gas to resemble a boiling liquid having a well defined level, maintaining said mass at reduction temperature, feeding nely divided ore to an upper portion of said mass, limiting back-mixing of solids in a vertical direction by obstructing the free, vertical flow of solids and gases at least at one point along their vertical path, withdrawing a gas mixture containing hydrogen and steam from an upper part of said reduction zone thereby establishing countercurrent flow of solids and gases within said yreduction zone, removing water from said gas mixture to obtain substantially dry hydrogen, recycling said dry hydrogen to the reduction zone, supplying the hydrogen produced by thermal decomposition of the hydrocarbon gas at a temperature not substantially below said decomposition temperature into the lower portion of said reduction zone to thereby supply a substantial portion of the heat required in the reduction of said f metal ore, correlating the supply of fresh hydrogen and the recycling of dry hydrogen to provide an amount of hydrogen in the reduction zone in excess of that required for reducing said ore to metal and to control the ratio of the partial pressure of hydrogen to the partial pressure of steam in the gas mixture withdrawn from the reduction zone and thereby maintain the atmosphere in said reduction zone capable of reducing the finely divided metal ore to metal and of preventing reoxidation of reduced metal within the reduction zone, withdrawing reduced metal from the bottom of said reduction zone, combining thermatomic carbon obtained by thermal decomposition of said hydrocarbon gas with said reduced metal and subjecting the resulting mixture to melting conditions in a melting zone.

11. The process as defined in claim 10 in which the ratio of the partial pressure of hydrogen to the partial pressure of steam in said withdrawn gas mixture falls within the approximate range of from 3 to 2 and the temperature in said reduction zone is maintained at about 700 to 900 C.

12. The process as defined in claim 11 in which said ore is an iron ore.

13. The process as dened in claim 11 in which said ore is an iron ore.

WARREN K. LEWIS.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,310,724 Westberg July 22, 1919 1,984,380 Odell Dec. 18, 1934 2,166,759 Greenawalt July 18, 1939 2,184,300 Hodson et al. Dec. 26, 1939 2,243,110 Madaras May 27, 1941 2,321,310 Moore June 8, 1943 2,343,780 Lewis Mar. 7, 1944 2,398,443 Munday Apr. 16, 1946 2,399,984 Caldwell May 7, 1946 2,438,584 Stewart Mar. 30,1948 2,444,990 Hemminger July 13, 1948 2,477,454 Heath July 26, 1949 2,481,217 Hemminger Sept. 6, 1949 2,538,201 Kalbach et al Jan. 16, 1951 2,559,631 Kalbach et al July 10, 1951 

1. A METHOD OF RECOVERING METAL FROM A SOLID, FINELY DIVIDED COMPOUND THEREOF WHICH IS REDUCIBLE TO METAL BY HYDROGEN WHICH COMPRISES MAINTAINING A DENSE, TURBULENT MASS OF SAID METAL COMPOUND FLUIDIZED BY AN UPWARDLY FLOWING GAS STREAM TO RESEMBLE A BOILING LIQUID HAVING A WELL DEFINED LEVEL WITHIN A REDUCTION ZONE AT REDUCTION TEMPERATURE, CAUSING SAID FLUIDIZED MASS OF METAL COMPOUND TO FLOW DOWNWARDLY AGAINST THE UPWARDLY FLOWING STREAM OF GAS, LIMITING THE BACK-MIXING OF SOLIDS IN A VERTICAL DIRECTION BY OBSTRUCTING THE FREE, VERTICAL FLOW OF SOLIDS AND GASES AT LEAST AT ONE POINT ALONG THEIR VERTICAL PATH WITHIN THE REDUCTION ZONE, CONTACTING SAID MASS WITH AN AMOUNT OF HYDROGEN IN EXCESS OF THAT REQUIRED FOR REDUCING SAID COMPOUND TO METAL, SUPPLYING HEATED FINELY DIVIDED METAL COMPOUND PARTICLES TO SAID REDUCTION ZONE, WITHDRAWING A GAS MIXTURE CONTAINING HYDROGEN AND STEAM FROM AN UPPER PORTION OF SAID REDUCTION 